When will memristors be ready for prime time?

The transistor was invented in 1925 but stayed dormant until finding a corporate champion in Bell Labs during the 1950s. Now another groundbreaking electronic circuit may be poised for the same kind of success after languishing as an academic curiosity for more than three decades.

Hewlett-Packard Labs is attempting to catapult the memristor, the fourth passive circuit element after resistors, capacitors and inductors, into the electronics mainstream. Invented in 1971, this "memory resistor" represents a potential revolution in electronic-circuit theory akin to the invention of the transistor—and perhaps its time has finally come. But as with that earlier device, it will take a killer application to get it off the ground.

Where the hearing aid played that role for the transistor, Hewlett-Packard Labs hopes resistive RAMs (RRAMs) will open the floodgates for the memristor. HP Labs is promising prototypes of these ultradense memory cells next year.

"I'd say memristors give HP a chance to become the dominant leader in memory technology in 10 years," said Martin Reynolds, vice president of Gartner Inc. "We have seen HP reinvent itself a number of times in the past, and this is a technology that could really drive that kind of change in the company again."

However, the clock is ticking. Last year, HP's crossbar switches—the building blocks of a new memory type the company is developing—were more than 20x denser than flash memories, giving HP breathing room to perfect its RRAMs. But in less than a year, flash memories have upped their density fourfold to eightfold by going to 2- and 3bit-per-cell configurations, respectively.

That unforeseen leap has narrowed HP's advantage. RRAMs now claim just 3x the density of flash, evoking memories of the same scenario that has doomed other next-generation memory technologies.

"When HP started work on the crossbar several years ago, they were 40- or 50x denser than flash," said Reynolds. "But now they are only about 3x denser than flash." To stay ahead, he said, HP will have to figure out how to boost the memristor's current density of 100Gbit/cm² "to a terabit in a square centimeter."

Waiting for killer appRegardless of whether HP's RRAMs become the killer application, the memristor could turn out to be as important a development as the transistor itself. And as with the transistor, applications may take a while to accumulate.

"The memristor's history is similar to that of the transistor, which was invented 35 years before its first major application," said Wolfgang Porod, an EE professor at Notre Dame University. Created in the 1920s by physicist Julius Edgar Lilienfeld, the device was not developed to its full potential until it came to the attention of Bell Labs researchers William Bradford Shockley, John Bardeen and Walter Houser Brattain, who were awarded the 1956 Nobel Prize for their pioneering work.